Oily residue under capcitiors of old main boards??

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Joined: Nov 22 2005
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I recently bought several early 90s Macs that have oil under the capcitiors. Is this some sort of pcb oil? They look ok and the boards work. Just oily. It's like under all areas of pcbs. What they heck is that??

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Joined: Apr 11 2012
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Re: Oily residue under capcitiors of old main boards??

I would check that the capacitors are not bulging or leaking. That is a common issue with old computer hardware, and although the boards still work fine they may be damaged by further capacitor decay if you don't replace damaged/dead capacitors.

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speedyG's picture
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Re: Oily residue under capcitiors of old main boards??

thats under normal condition not oil, but in fact that capacitors are leaking and that stuff is borium-acid....
additional remark: this happens to nearly all electrolytic-capacitors ( that are those with a + and a - polarity )
and the acid is used in them as electrolytic-fluid..... that stuff can etch by time copper-leads away. This means as mentioned in a later post that the liquid must by cleaned away with anionic fluid like dishwasher that neutrolizes the acid and stops the etching process. After cleaning and drying it is recommended to mark close to the capacitor the values ( xxµf / XX V ) = ( capacity / voltagelimit ) and the polarity ( side where + is and side where - is. I do this with waterproof CD markerpen.
There after the capacitor can be replaced with the same value of capacity and at least the same voltagelimit or next step above as explained in later posting.
Be sure that - marking at the capacitor ( - ) is in same position as the one replaced ! Wrong polarity makes those capacitors explode with loud popping and the borium acid will be spitting around the whole area.... this will damage the computer !

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Joined: Apr 11 2012
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Re: Oily residue under capcitiors of old main boards??

I agree with you speedyG. I have seen a lot of old Macs get dumped into the trash because people have not thought to check out the capacitors when troubleshooting. 2 times out of 3 all you have to do is wash the motherboard (Some use a dishwasher, others use rubbing alcohol and Q-Tips) and replace the capacitors on the board (Or if you are not very good at soldering like me get someone else to replace the capacitors).

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Joined: May 7 2006
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Re: Oily residue under capcitiors of old main boards??

Just curious, what kind of caps should you replace them with?

If I'm having to recap a motherboard, I only want to do it once every 10-15 years or so.

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eeun's picture
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Re: Oily residue under capcitiors of old main boards??

You'll want to make sure you get the same capacitance, but it doesn't hurt getting a higher (but not lower) voltage rating.
For example, it's acceptable to replace a 47uf 16V cap with a 47uf 25V one.

I did my 840av recently, and bought all the capacitors off a Hong Kong ebay seller. Recommend buying a few more than you need, just in case of accidents.

A capacitor list of a number of older Macs, along with some handy tips, is here:
http://68kmla.org/wiki/Capacitor_Replacement

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Joined: Nov 22 2005
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Re: Oily residue under capcitiors of old main boards??

So possible that every single capacitor on the main board is leaking but not showing anything like bulding or anything and on several boards?

eeun's picture
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Re: Oily residue under capcitiors of old main boards??

Maybe not all of them are leaking, but the usual procedure is to replace them all.
For one, you've already got the computer apart, the soldering iron out, etc. And how long are the remaining caps going to last, given that their neighbours of the same type and age are failing?

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Joined: Apr 11 2012
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Re: Oily residue under capcitiors of old main boards??

Someone with more experience may be able to correct me on this one, but wouldn't the ideal situation be to replace the capacitors with the new solid type ones? My reasoning behind this theory is that surely using the solid type capacitors would reduce (prevent?) further issues due to leaking capacitors. And before you say anything about the solid capacitors not being suitable for motherboard use, most modern motherboards (at least in Australia anyway) are built using these solid capacitors to increase the board lifespan and reduce the risk of board damage.

Edit: The only trouble I can seem to think of when using solid capacitors is that if one of the new capacitors dies (or is faulty) there will be little to no external signs.

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eeun's picture
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Re: Oily residue under capcitiors of old main boards??

I think you may have some misconceptions about which capacitors are 'solid'. I haven't seen any modern consumer motherboard that doesn't have a good number of electrolytic (ie - wet) capacitors onboard. It's safe to assume a can shape = electrolytic = liquid.

In some instances it's possible to swap with some other polarized capacitor like tantalums, and those are available at similar capacitance/voltage ratings. Depending on what the cap is being used for on the board, including the amount of inrush current it may experience, a tantalum may not be suitable. Hoping someone like Trag with more knowledge than me will read this and clarify.

If you choose a capacitor different from the original, you'll also have to deal with fit issues. Depending on the Mac board, some of those pads seem to lift from the board in a light breeze. Any less contact area with a substitute cap may risk having them pop off and taking a trace with them at the slightest bump during cleaning, reassembly, etc. Also, Apple's boards were multi-layer, so there's no way you could safely drill holes for non-SMT components.

I'd really recommend sticking with what's known to work. You'll keep your board stock and with the proper new caps, any problems you face at reassembly will be easier to diagnose. If all it needs is re-capping in another 20-ish years, I'd consider that pretty good mileage.

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